The present invention relates to headlamps for motor vehicle use, and more particularly to a projector type headlamp for a motor vehicle in which the output light beam of a light source is converted into a parallel light beam by means of an elliptical mirror and a condenser lens so as to illuminate the area in front of the motor vehicle.
In a projector type headlamp an elliptical mirror is arranged in a lamp chamber defined by a lamp body and a front lens covering the front opening of the lamp body, and a light bulb is installed at the first focal point of the elliptical mirror. A condenser lens is disposed in such a manner that its focal point is substantially at the second focal point of the elliptical mirror. The rays of light from the light bulb are reflected by the elliptical mirror, and gathered in a narrow space around the optical axis by the condenser lens into parallel rays of light. The condenser lens is a convex lens whose front surface is a convex surface such as a paraboloidal. An extension is provided around the condenser lens, thus closing the space between the condenser lens and the front peripheral portion of the lamp body. The projector type headlamp is advantageous in that it is small in size and a desired distribution of light can be obtained.
FIG. 10 is a sectional view showing essential components of an example of a conventional extension-mounted structure (see, for instance, U.S. Pat. No. 4,727,458). In FIG. 10, reference numeral 1 designates a vehicle body; 2, a lamp body mounted on the vehicle body 1; 3, a front lens covering the front opening 4 of the lamp body 2; 5, an elliptical mirror; 6, a condenser lens; and 7, an extension. The extension 7 is fixedly installed in the lamp by fixedly bonding the peripheral portion of the extension 7 to the flange-like front end portion of the lamp body 2 with an adhesive or the like, and the peripheral wall of the front lens 3 is fixedly fitted in the front end portion of the lamp body 2 with the extension 7 held between the flange-like front end portion of the lamp body 2 and the end face of the peripheral wall of the front lens 3.
However, the above-described conventional extension mounting structure suffers from the certain difficulties. First, surface alignment of the lamp body 2 and the front lens 3 is difficult. Furthermore, it is rather difficult to rigidly couple the front lens 3 to the lamp body 2. That is, in the application of the adhesive, the lamp body 2 may be made fouled thereby unless the operator is very careful. Also, the adhesive tends to deteriorates with time, so that the extension 7 may come off the lamp body 2.